Recently the use of asymmetric septal hypertrophy, detected by echocardiography, has led to the recognition of a broad pathophysiologic spectrum of hypertrophic cardiomyopathy. We examined the prevalence and diagnostic usefulness of electrocardiographic abnormalities in a large, diverse group of patients with hypertrophic cardiomyopathy, and related the electrocardiographic abnormalities to symtomatic status as well as echocardiographic and hemodynamic findings. The high prevalence and protean nature of electrocardiographic abnormalities found suggest that any patient with an unusual and unexplained electrocardiogram should be suspected of having hypertrophic cardiomyopathy even if his physical examination is normal, as is often the case in patients without obstruction.